Please post pictures of your previous cars if you can!
Why did you get rid of the 2015 GT? What did you think of the coyote engine and the IRS? Did you run into any issues at all? What was your MPG?
Since your car did not come with a Cobb AP, I heavily recommend you source a stock intake to put install back on the car. You can either sell the Perrin intake or keep it for a later point in time if you think you're going to buy a Cobb AP in the future. I believe one of the OTS (Off The Shelf) maps that Cobb has is for a Stage 1 Perrin intake. You'll have to look on their website for the exact details since I'm recalling from memory.
By having an intake, but no tune to compensate for it, the engine is not in harmony and you can cause issues. If you're new to the Subaru platform with no previous knowledge, I recommend you read our sticky threads.